Best Cobalt Drill Bit Sets for Hardened Steel: A Comparison of M35 and M42 Options
Selecting the right drill bit for hardened steel requires a focus on material composition and heat resistance. Cobalt steel, specifically M35 and M42 grades, provides the necessary hardness to penetrate tough metals without premature dulling. When working with hardened steel, stainless steel, or cast iron, the coating and tip geometry are critical factors that influence performance and longevity. TiAlN (Titanium Aluminum Nitride) coatings are frequently used to enhance heat resistance, while split points and specialized tip designs help prevent walking on the surface. This guide compares several popular cobalt sets to help you determine which features best align with your specific drilling requirements, ranging from standard jobber lengths to compact, hex-shank stubby bits.
When drilling into demanding materials like hardened steel or titanium, the mechanical configuration of the bit matters as much as the alloy itself. Features such as three-flat shanks provide improved chuck grip, while varied tip designs, including stepped points or bullet points, assist with precision and self-centering. Whether you need an extensive 21-piece indexed collection for a wide range of hole sizes or a compact 8-piece set for specific applications, the following breakdown highlights the technical specifications of each kit. Evaluate these options based on your equipment compatibility, such as hex-shank versus round-shank requirements, to ensure a secure and efficient drilling experience in your workshop.
1. 14Pcs M35 Cobalt Drill Bit Set (Pro), 1/16"-1/2", TiAlN Coat, 3-Flats Shank | 135° Split Point, Jobber Twist Metal Drill Bit Set with Storage Case, for Hardened Metal & Stainless Steel, Wood & Plastic
This 14-piece set features M35 cobalt steel construction finished with a TiAlN coating, designed to manage the high heat generated when drilling into hardened metal and stainless steel. The bits range from 1/16-inch to 1/2-inch, following a standard jobber twist design. Each bit includes a 135-degree split point, which is intended to reduce the need for center punching by preventing the bit from walking on the material surface. The inclusion of a 3-flat shank is intended to provide a more secure grip in standard drill chucks, limiting slippage during heavy-duty tasks. The set is supplied with a storage case for organization and is also marketed for use on softer materials like wood and plastic, offering versatility across different workshop projects.
Best for: General purpose metal drilling requiring a variety of sizes
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- M35 cobalt steel construction
- TiAlN heat-resistant coating
- 135-degree split point geometry
- 3-flat shank for secure chuck grip
Keep in mind
- Limited to a 14-piece range
- May not offer the same longevity as M42 steel
2. Crosstar 21Pc Cobalt Stepped Point Drill Bit Set,1/16-1/2" TiAlN Coated | Step Dill Head,M35 HSS Jobber Bits,No Pre-Drilling,3-Flat Shank,with Indexed Storage Case,Precise Drilling,for Hardened Steel
This 21-piece set utilizes M35 cobalt HSS in a jobber length, incorporating a stepped point drill head design. The primary advantage of the stepped point is the potential to eliminate the need for pre-drilling, as the geometry is engineered to start holes more effectively on hard surfaces. With a size range of 1/16-inch to 1/2-inch, the set includes an indexed storage case for quick selection. The bits feature a TiAlN coating to assist with thermal management during operation. A 3-flat shank is utilized to maintain compatibility with standard power drill chucks while minimizing rotation under load. These bits are specifically targeted toward hardened steel applications where precision and ease of entry are prioritized over traditional twist bit designs.
Best for: Precision drilling without the need for pilot holes
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- 21-piece comprehensive size range
- Stepped point head design
- TiAlN coated M35 cobalt steel
- 3-flat shank for stability
Keep in mind
- Lower user rating compared to other sets
- Stepped geometry may require specific technique
3. Crosstar 8Pc M35 Cobalt Stubby Drill Bit Set for Hard Metals, 3/32"-3/8" | Metal Drill Bits, TiAlN Coated, 1/4" Hex Shank, for Hardened Steel, Stainless Steel, Cast Iron, Titanium, Light-Gauge Metal
Optimized for portability and compatibility with impact drivers, this 8-piece set features M35 cobalt stubby bits with a 1/4-inch hex shank. The stubby length is intended to provide higher rigidity and reduce deflection when drilling into tough materials like hardened steel, stainless steel, cast iron, and titanium. The TiAlN coating provides a protective barrier against the heat generated during high-friction metalworking. Because these bits use a hex shank, they are well-suited for quick-change chucks commonly found on cordless drivers. This set is a specialized solution for users who prioritize compact tool length and rapid bit changes in tight or light-gauge metal applications, though the size range is more limited than standard jobber sets.
Best for: Users of impact drivers and tight-space drilling
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- 1/4-inch hex shank for quick changes
- Stubby length for increased rigidity
- M35 cobalt with TiAlN coating
- Versatile across various hard metals
Keep in mind
- Smaller 8-piece size range
- Stubby design limits maximum hole depth
4. BOSCH CO14B 14-Piece Cobalt Drill Bit Set with Included Case - M42 Metal Drill Bits with Three-Flat Shank for Drilling Applications in Stainless Steel, Cast Iron, Titanium, and Light-Gauge Metal
This 14-piece set from Bosch features M42 cobalt steel, which generally offers higher heat resistance and durability than standard M35 alloys. The set includes a storage case and bits configured with a 3-flat shank to prevent slippage in drill chucks. These bits are intended for challenging drilling applications involving stainless steel, cast iron, titanium, and light-gauge metals. By utilizing the M42 grade, the manufacturer emphasizes the ability to withstand the stresses of drilling into dense, hardened materials. The set provides a balanced selection of sizes for standard workshop use, backed by a higher customer satisfaction rating compared to several M35-based alternatives. The inclusion of the 3-flat shank ensures that the bits remain centered and stable during operation.
Best for: Heavy-duty applications requiring premium M42 cobalt
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- Durable M42 cobalt steel alloy
- Includes protective storage case
- 3-flat shank design
- High user satisfaction rating
Keep in mind
- 14-piece set may be too small for some
- Higher cost point potentially expected
5. Crosstar 21Pcs M35 Cobalt Drill Bit Set,1/16"-1/2" Metal Drill Bits | TiAlN Coated,Bullet Point Tip,Self-Centering High-Speed Steel Jobber Bits,for Thin Hardened Steel,Stainless Steel,Titanium
This 21-piece set features M35 cobalt bits with a specialized bullet point tip. The tip design is engineered for self-centering, which is particularly useful when working on thin hardened steel or stainless steel where bit wandering can damage the workpiece. The bits are TiAlN coated to enhance performance and longevity when drilling through titanium and other high-strength materials. The set covers a range from 1/16-inch to 1/2-inch, providing a comprehensive selection for varied project demands. These jobber-length bits are designed as high-speed steel components that prioritize ease of starting and centering. The set includes an indexed storage case, allowing for systematic organization and rapid access during complex drilling tasks involving thin-gauge metals.
Best for: Self-centering applications on thin, hard materials
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- Bullet point tip for self-centering
- 21-piece indexed storage case
- TiAlN coated M35 cobalt steel
- Jobber length for standard depth
Keep in mind
- Bullet point tip may wear differently than standard points
- Performance on very thick hardened steel is not specified
How to choose
Material Composition
When selecting drill bits for hardened steel, material composition is the primary factor. M35 cobalt steel is the industry standard for these applications, offering higher heat resistance and durability compared to standard high-speed steel. For even greater performance, some professional-grade sets, such as the Bosch CO14B, utilize M42 cobalt, which is renowned for its ability to withstand the extreme temperatures generated when drilling into tough, dense alloys. Always verify the cobalt grade, as the alloying elements directly correlate to the bit's ability to maintain a sharp cutting edge without deforming under the high pressure required to penetrate hardened metal surfaces.
Coating Technologies
Surface coatings significantly extend the lifespan of drill bits used on hardened steel. Many current options, such as the 14-piece M35 cobalt set or the Crosstar 21-piece collection, feature a Titanium Aluminum Nitride (TiAlN) coating. This specific treatment provides superior oxidation resistance and hardness compared to standard titanium nitride. Because hardened steel generates intense friction, a high-quality TiAlN coating acts as a thermal barrier, preventing the bit from softening during operation. When comparing sets, prioritize those explicitly featuring TiAlN coatings to ensure the drill bits can handle the abrasive nature of hardened steel, stainless steel, and cast iron effectively.
Shank Design
The shank design dictates how securely the bit fits into your power tool's chuck. A 3-flat shank is highly recommended for drilling hardened steel because it prevents the bit from spinning inside the chuck when under heavy torque. This feature is common across many M35 cobalt sets, including both the 14-piece and 21-piece options. Alternatively, some specialized sets, such as the Crosstar 8-piece stubby set, utilize a 1/4-inch hex shank, which is ideal for impact drivers and quick-change chucks. Choosing the correct shank ensures power transmission efficiency and minimizes the risk of bit slippage during demanding metal drilling tasks.
Point Geometry
The geometry of the drill bit tip determines how easily the tool initiates a hole in hard surfaces. Split point designs, such as the 135-degree angle found on the 14-piece M35 set, are engineered to prevent 'walking' across the metal surface, allowing for precise starts without the need for a center punch. Other variations include stepped points or bullet point tips, which assist with self-centering and eliminate the need for pre-drilling. When working with thin or hardened steel, selecting a bit with an advanced point geometry reduces the physical effort required to start the hole and increases the overall accuracy of your finished work.
Bit Length and Configuration
The physical length of the drill bit impacts its stability and suitability for different tasks. Jobber length bits are the standard choice for general-purpose drilling, offering a versatile reach for most metalworking projects. However, for applications where vibration must be minimized, stubby drill bits like the Crosstar 8-piece set are superior. Their shorter length increases rigidity, which is crucial when applying the high pressure needed to penetrate hardened steel. Evaluate your project workspace to determine if you require the extended reach of a jobber bit or the increased structural stability of a shorter, stubby configuration to achieve the cleanest results.
Frequently asked questions
What is the difference between M35 and M42 cobalt drill bits?
M35 cobalt steel contains 5% cobalt, providing excellent heat and wear resistance suitable for hardened steel and stainless steel. M42 cobalt, such as that found in the Bosch CO14B set, contains 8% cobalt. This higher concentration allows the tool to maintain hardness at even higher temperatures, making it a robust choice for heavy-duty applications involving titanium, cast iron, and extremely hardened metals where heat buildup is constant.
Do I need a special drill bit for thin hardened steel?
Yes, for thin materials, look for bits with specialized tips like the bullet point design found in the Crosstar 21-piece set. These bits are engineered to be self-centering, which is critical when drilling thin sheets to prevent the bit from grabbing or tearing the metal. Additionally, using a TiAlN-coated cobalt bit ensures the tool can withstand the friction without overheating, maintaining a clean entry point on thin-gauge hardened steel surfaces.
Can I use these cobalt bits in an impact driver?
Standard round-shank or 3-flat shank cobalt bits are generally designed for drill presses or traditional drill chucks. If you are using an impact driver, you should choose a set with a 1/4-inch hex shank, such as the Crosstar 8-piece stubby set. The hex shank is specifically compatible with impact driver quick-change systems, ensuring the bit remains secure and stable while you drill into hard metals like stainless steel or cast iron.
Why do some drill bits have a 3-flat shank?
A 3-flat shank is a design feature intended to provide a superior grip within the drill chuck. When drilling into hardened steel, high torque is required, which can cause standard cylindrical shanks to slip or spin. The three flat surfaces allow the chuck jaws to lock onto the bit firmly, preventing rotation slippage. This design is standard in many professional M35 cobalt sets to ensure consistent power transfer during difficult drilling operations.
Are these cobalt bits suitable for drilling wood and plastic?
While cobalt bits are primarily engineered for hardened steel, stainless steel, and titanium, many sets—such as the 14-piece M35 Cobalt Drill Bit Set—are also rated for use on wood and plastic. However, because they are optimized for the high heat and resistance of metal, they may be overkill for softer materials. If you choose to use them on wood or plastic, they will perform effectively, but they are specifically constructed to handle the rigors of metalworking.
Bottom line
For the most demanding applications involving hardened steel, the Bosch CO14B 14-Piece Cobalt Drill Bit Set stands out due to its M42 cobalt composition. This material grade offers higher heat resistance than standard M35 options, making it the most resilient choice for high-friction tasks involving titanium, stainless steel, and cast iron. While other sets like the Crosstar 21-piece collection offer excellent versatility with self-centering bullet points and TiAlN coatings, the Bosch set’s focus on M42 material provides a premium performance edge. For users who prioritize longevity and thermal stability when tackling the toughest metal surfaces, this set provides a reliable foundation, backed by a strong 4.6-star rating that reflects its professional-grade capabilities.
Deciding between these sets depends on your specific tool setup and the thickness of the metal. If you are using an impact driver, the Crosstar 8-piece stubby set with its 1/4-inch hex shank is the clear winner for stability and compatibility. For general workshop needs, compare the 14-piece and 21-piece jobber sets based on the range of diameters you require. If you frequently struggle with bits wandering on the surface, prioritize the Crosstar 21-piece sets, as their bullet or stepped point designs are specifically engineered to simplify the starting process. Match the shank type to your drill chuck, and always opt for TiAlN-coated cobalt bits to ensure the best durability against hardened steel.
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